Bra*_*Mcq 2 multithreading nsurlrequest ios nscondition
我正在通过互联网异步下载四个 plist 文件。我需要等到所有四个文件都下载完毕，直到我在第一次运行时推送 UIViewController 或在所有后续运行中刷新数据并重新加载我的所有 UITableViews。
在第一次运行时，一切正常。刷新时，所有四个 url 请求都被调用和启动，但从不调用它们的完成或失败块，并且 UI 冻结。这很奇怪，因为我在后台线程中执行所有操作。我一直无法弄清楚为什么会发生这种情况。
第一次加载和刷新方法以相同的方式调用四个“更新”方法，并以相同的方式使用 NSCondition。
对于第一次运行：
- (void)loadContentForProgram:(NSString *)programPath
{
NSLog(@"Start Load Program");
AppDelegate *myDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
hud = [[MBProgressHUD alloc] initWithView:myDelegate.window];
[myDelegate.window addSubview:hud];
hud.labelText = @"Loading...";
hud.detailsLabelText = @"Loading Data";
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
//Do stuff here to load data from files
//Update From online files
hud.detailsLabelText = @"Updating Live Data";
resultLock = NO;
progressLock = NO;
recallLock = NO;
stageLock = NO;
condition = [[NSCondition alloc] init];
[condition lock];
[self updateCurrentCompsText];
[self updateCompetitionResults];
[self updateCompetitionRecalls];
[self updateCompetitionProgress];
while (!resultLock) {
[condition wait];
}
NSLog(@"Unlock");
while (!stageLock) {
[condition wait];
}
NSLog(@"Unlock");
while (!recallLock) {
[condition wait];
}
NSLog(@"Unlock");
while (!progressLock) {
[condition wait];
}
NSLog(@"Unlock");
[condition unlock];
updateInProgress = NO;
//Reset Refresh controls and table views
self.refreshControlsArray = [[NSMutableArray alloc] init];
self.tableViewsArray = [[NSMutableArray alloc] init];
NSLog(@"Finished Loading Program");
[[NSNotificationCenter defaultCenter] postNotificationName:@"WMSOFinishedLoadingProgramData" object:nil]; //Pushes view controller
dispatch_async(dispatch_get_main_queue(), ^{
[MBProgressHUD hideHUDForView:myDelegate.window animated:YES];
});
});
}
刷新数据时：
- (void)updateProgramContent
{
if (!updateInProgress) {
updateInProgress = YES;
for (int i = 0; i < self.refreshControlsArray.count; i++) {
if (!((UIRefreshControl *)self.refreshControlsArray[i]).refreshing) {
[self.refreshControlsArray[i] beginRefreshing];
[self.tableViewsArray[i] setContentOffset:CGPointMake(0.0, 0.0) animated:YES];
}
}
resultLock = NO;
stageLock = NO;
recallLock = NO;
progressLock = NO;
dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
condition = [[NSCondition alloc] init];
[condition lock];
[self updateCompetitionProgress];
[self updateCompetitionRecalls];
[self updateCompetitionResults];
[self updateCurrentCompsText];
while (!resultLock) {
[condition wait];
}
NSLog(@"Unlock");
while (!stageLock) {
[condition wait];
}
NSLog(@"Unlock");
while (!recallLock) {
[condition wait];
}
NSLog(@"Unlock");
while (!progressLock) {
[condition wait];
}
NSLog(@"Unlock");
[condition unlock];
});
for (int i = 0; i < self.refreshControlsArray.count; i++) {
[self.refreshControlsArray[i] performSelector:@selector(endRefreshing) withObject:nil afterDelay:1.0];
[self.tableViewsArray[i] performSelector:@selector(reloadData) withObject:nil afterDelay:1.0];
}
updateInProgress = NO;
}
}
下面的块出现在上面的每个加载方法中，对应于将下载和更新特定数据的方法。
[self updateCompetitionProgress];
[self updateCompetitionRecalls];
[self updateCompetitionResults];
[self updateCurrentCompsText];
运行：
- (void)updateCompetitionResults
{
__block NSDictionary *competitionResultsData = nil;
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"Some URL",[self.programName stringByReplacingOccurrencesOfString:@" " withString:@"%20"]]] cachePolicy:NSURLCacheStorageNotAllowed timeoutInterval:20.0];
AFPropertyListRequestOperation *operation = [AFPropertyListRequestOperation propertyListRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id propertyList) {
competitionResultsData = (NSDictionary *)propertyList;
[competitionResultsData writeToFile:[@"SOME LOCAL PATH"] atomically:NO];
[self updateCompetitionResultsWithDictionary:competitionResultsData];
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id propertyList) {
competitionResultsData = [NSDictionary dictionaryWithContentsOfFile:[@"SOME LOCAL PATH"]];
NSLog(@"Failed to retreive competition results: %@", error);
[self updateCompetitionResultsWithDictionary:competitionResultsData];
}];
[operation start];
}
并且完成块和失败块调用相同的方法来更新数据
- (void)updateCompetitionResultsWithDictionary:(NSDictionary *)competitionResultsData
{
//Do Stuff with the data here
resultLock = YES;
[condition signal];
}
那么，为什么这在第一次运行时有效，但在任何后续运行中都不起作用？
正如我在上面的评论中提到的，最明显的问题是您正在调用condition在 initialize 之前使用的方法condition。确保condition在开始调用之前进行初始化updateCompetitionResults等。
就更彻底的变化而言，我可能建议NSCondition完全退休，并使用操作队列：
我可能会使用NSOperationQueue（或者你也可以使用调度组，如果你愿意，但我喜欢操作队列的能力来配置你可以操作多少并发操作......如果你到了想要取消操作的地步，我认为NSOperationQueue那里也提供了一些不错的功能）。然后，您可以将每个下载和处理定义为单独的NSOperation（每个下载应该同步发生，因为它们在操作队列中运行，您可以获得异步操作的好处，但是您可以在下载完成）。然后，您只需将它们排队以异步运行，但定义一个依赖于其他四个的最终操作，一旦完成四个下载就会开始。（顺便说一下，我用NSBlockOperation它为NSOperation对象提供了块功能，但您可以以任何方式进行。）
虽然您updateProgramContent可能会异步下载，但它会依次处理四个下载的文件，一个接一个。因此，如果第一次下载需要一段时间才能下载，它将阻止其他人的后期处理。相反，我喜欢将四个 plist 文件中的NSOperation每一个的下载和后期处理都封装在一个. 因此，我们不仅享受下载的最大并发性，也享受后处理的最大并发性。
而不是使用AFNetworking（这通常我的大风扇）的plist相关的方法，我可能会倾向于使用NSDictionary和NSArray功能，让您从网络上下载的plist，并将它们加载到相应的结构。这些dictionaryWithContentsOfURL并arrayWithContentsOfURL同步运行，但因为我们在后台操作中执行此操作，所以一切都像您想要的那样异步运行。这也绕过了将它们保存到文件的过程。如果您希望将它们保存到目录中的文件中Documents，您也可以轻松做到。显然，如果您在下载 plist 文件时正在做一些复杂的事情（例如，您的服务器正在进行一些质询-响应身份验证），则无法使用方便NSDictionary和NSArray方法。但如果你不需要所有这些，简单的NSDictionary和NSArray方法，___WithContentsOfURL让生活变得非常简单。
将所有这些放在一起，它可能看起来像：
@interface ViewController ()
@property (nonatomic, strong) NSArray *competitions;
@property (nonatomic, strong) NSDictionary *competitionResults;
@property (nonatomic, strong) NSDictionary *competitionRecalls;
@property (nonatomic, strong) NSDictionary *competitionProgress;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self transfer];
}
- (void)allTransfersComplete
{
BOOL success;
if (self.competitions == nil)
{
success = FALSE;
NSLog(@"Unable to download competitions");
}
if (self.competitionResults == nil)
{
success = FALSE;
NSLog(@"Unable to download results");
}
if (self.competitionRecalls == nil)
{
success = FALSE;
NSLog(@"Unable to download recalls");
}
if (self.competitionProgress == nil)
{
success = FALSE;
NSLog(@"Unable to download progress");
}
if (success)
{
NSLog(@"all done successfully");
}
else
{
NSLog(@"one or more failed");
}
}
- (void)transfer
{
NSURL *baseUrl = [NSURL URLWithString:@"http://insert.your.base.url.here/competitions"];
NSURL *competitionsUrl = [baseUrl URLByAppendingPathComponent:@"competitions.plist"];
NSURL *competitionResultsUrl = [baseUrl URLByAppendingPathComponent:@"competitionresults.plist"];
NSURL *competitionRecallsUrl = [baseUrl URLByAppendingPathComponent:@"competitionrecalls.plist"];
NSURL *competitionProgressUrl = [baseUrl URLByAppendingPathComponent:@"competitionprogress.plist"];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.maxConcurrentOperationCount = 4; // if your server doesn't like four concurrent requests, you can ratchet this back to whatever you want
// create operation that will be called when we're all done
NSBlockOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
// any stuff that can be done in background should be done here
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// any user interface stuff should be done here; I've just put this in a separate method so this method doesn't get too unwieldy
[self allTransfersComplete];
}];
}];
// a variable that we'll use as we create our four download/process operations
NSBlockOperation *operation;
// create competitions operation
operation = [NSBlockOperation blockOperationWithBlock:^{
// download the competitions and load it into the ivar
//
// note, if you *really* want to download this to a file, you can
// do that when the download is done
self.competitions = [NSArray arrayWithContentsOfURL:competitionsUrl];
// if you wanted to do any post-processing of the download
// you could do it here.
NSLog(@"competitions = %@", self.competitions);
}];
[completionOperation addDependency:operation];
// create results operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionResults = [NSDictionary dictionaryWithContentsOfURL:competitionResultsUrl];
NSLog(@"competitionResults = %@", self.competitionResults);
}];
[completionOperation addDependency:operation];
// create recalls operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionRecalls = [NSDictionary dictionaryWithContentsOfURL:competitionRecallsUrl];
NSLog(@"competitionRecalls = %@", self.competitionRecalls);
}];
[completionOperation addDependency:operation];
// create progress operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionProgress = [NSDictionary dictionaryWithContentsOfURL:competitionProgressUrl];
NSLog(@"competitionProgress = %@", self.competitionProgress);
}];
[completionOperation addDependency:operation];
// queue the completion operation (which is dependent upon the other four)
[queue addOperation:completionOperation];
// now queue the four download and processing operations
[queue addOperations:completionOperation.dependencies waitUntilFinished:NO];
}
@end
现在，我不知道您的 plist 中哪些是数组，哪些是字典（在我的示例中，我将比赛设为数组，其余是由比赛 ID 键控的字典），但希望您了解我在拍摄什么为了。最大化并发，消除NSCondition逻辑，真正充分利用NSOperationQueue等。
这可能需要考虑的太多了，但我只提到它作为NSCondition. 如果您目前的技术有效，那就太好了。但上面概述了我将如何应对这样的挑战。
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